10.0.21.208/28
Private (RFC 1918) RFC 1918Class A — /28 prefix — 14 usable hosts
Network address — the base address of the block (10.0.21.208). All devices in this subnet share this prefix. Cannot be assigned to a host.
Broadcast address — packets sent to 10.0.21.223 are delivered to every device in the subnet. Also reserved — not assignable.
Usable hosts — the 14 addresses between those two that you can assign to servers, VMs, or interfaces.
Subnet mask — 255.255.255.240 is the dotted-decimal equivalent of /28. Older tools and Cisco configs use this format instead of CIDR slash notation.
Full Details
| CIDR Notation | 10.0.21.208/28 |
| Network Address | 10.0.21.208 |
| Broadcast Address | 10.0.21.223 |
| Subnet Mask | 255.255.255.240 |
| Wildcard Mask | 0.0.0.15 |
| Prefix Length | /28 |
| IP Address Class | Class A |
| Total IP Addresses | 16 |
| Usable Host Addresses | 14 |
| First Usable IP | 10.0.21.209 |
| Last Usable IP | 10.0.21.222 |
| Network (Hex) | 0x0A0015D0 |
| Broadcast (Hex) | 0x0A0015DF |
| Governing RFC | RFC 1918 |
| Address Type | Private (RFC 1918) |
Binary Representation
The first 28 bits (1s in the mask) identify the network. The remaining 4 bits identify hosts within the network.
Subnet Breakdown — splitting into /29
This /28 block can be divided into 2 /29 subnets.
| CIDR | Network | Broadcast | First Usable | Last Usable | Hosts |
|---|---|---|---|---|---|
| 10.0.21.208/29 | 10.0.21.208 | 10.0.21.215 | 10.0.21.209 | 10.0.21.214 | 6 |
| 10.0.21.216/29 | 10.0.21.216 | 10.0.21.223 | 10.0.21.217 | 10.0.21.222 | 6 |